Method and apparatus for generating a phy data unit

ABSTRACT

A first legacy portion of a physical layer (PHY) preamble is generated, wherein the first legacy portion of the PHY preamble is generated to include a signal field having PHY parameters arranged in subfields according to a first legacy communication protocol. A second portion of the PHY preamble is generated according to a second communication protocol, wherein the second portion of the PHY preamble is generated to include a repetition of the signal field. A PHY data unit that includes the PHY preamble is generated, the PHY data unit being for transmission via a wireless communication channel.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a continuation of U.S. application Ser. No.13/366,064, entitled “Control Mode PHY for WLAN,” filed Feb. 3, 2012,now U.S. Pat. No. 9,130,727, which claims the benefit of the followingU.S. Provisional Patent Applications:

-   -   U.S. Provisional Patent Application No. 61/439,777, entitled        “11ah OFDM Low Rate PHY,” filed on Feb. 4, 2011;

U.S. Provisional Patent Application No. 61/440,804, entitled “11ah OFDMLow Rate PHY,” filed on Feb. 8, 2011;

-   -   U.S. Provisional Patent Application No. 61/454,444, entitled        “11ah OFDM Low Rate PHY,” filed on Mar. 18, 2011;    -   U.S. Provisional Patent Application No. 61/477,076, entitled        “11ah OFDM Low Rate PHY,” filed on Apr. 19, 2011;    -   U.S. Provisional Patent Application No. 61/480,238, “11ah OFDM        Low Rate PHY,” filed on Apr. 28, 2011;    -   U.S. Provisional Patent Application No. 61/490,447, entitled        “11ah OFDM Low Rate PHY,” filed on May 26, 2011;    -   U.S. Provisional Patent Application No. 61/492,464, entitled        “11ah OFDM Low Rate PHY,” filed on Jun. 2, 2011;    -   U.S. Provisional Patent Application No. 61/499,964, entitled        “11ah OFDM Low Rate PHY,” filed on Jun. 22, 2011;    -   U.S. Provisional Patent Application No. 61/500,505, entitled        “11ah OFDM Low Rate PHY,” filed on Jun. 23, 2011;    -   U.S. Provisional Patent Application No. 61/515,244, entitled        “11ah OFDM Low Rate PHY,” filed on Aug. 4, 2011; and    -   U.S. Provisional Patent Application No. 61/524,263, entitled        “11ah OFDM Low Rate PHY,” filed on Aug. 16, 2011.

The disclosures of all of the above-referenced patent applications arehereby incorporated by reference herein in their entireties.

The present application is also related to U.S. patent application Ser.No. 13/366,038, entitled “Control Mode PHY for WLAN,” filed on Feb. 3,2012, now U.S. Pat. No. 8,885,740, which is hereby incorporated byreference herein in its entirety.

FIELD OF THE DISCLOSURE

The present disclosure relates generally to communication networks and,more particularly, to long range low power wireless local area networks.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent it is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

When operating in an infrastructure mode, wireless local area networks(WLANs) typically include an access point (AP) and one or more clientstations. WLANs have evolved rapidly over the past decade. Developmentof WLAN standards such as the Institute for Electrical and ElectronicsEngineers (IEEE) 802.11a, 802.11b, 802.11g, and 802.11n Standards hasimproved single-user peak data throughput. For example, the IEEE 802.11bStandard specifies a single-user peak throughput of 11 megabits persecond (Mbps), the IEEE 802.11a and 802.11g Standards specify asingle-user peak throughput of 54 Mbps, the IEEE 802.11n Standardspecifies a single-user peak throughput of 600 Mbps, and the IEEE802.11ac Standard specifies a single-user peak throughput in the Gbpsrange.

Work has begun on a two new standards, IEEE 802.11ah and IEEE 802.11af,each of which will specify wireless network operation in sub-1 GHzfrequencies. Lowe frequency communication channels are generallycharacterized by better propagation qualities and extended propagationranges compared to transmission at higher frequencies. In the past,sub-1 GHz ranges have not been utilized for wireless communicationnetworks because such frequencies were reserved for other applications(e.g., licensed TV frequency bands, radio frequency band, etc.). Thereare few frequency bands in the sub 1-GHz range that remain unlicensed,with different specific unlicensed frequencies in different geographicalregions. The IEEE 802.11ah Standard will specify wireless operation inavailable unlicensed sub-1 GHz frequency bands. The IEEE 802.11afStandard will specify wireless operation in TV White Space (TVWS), i.e.,unused TV channels in sub-1 GHz frequency bands.

SUMMARY

In one embodiment, a method includes: generating, at a network interfacedevice, a first legacy portion of a physical layer (PHY) preamble,wherein the first legacy portion of the PHY preamble is generated toinclude a signal field having PHY parameters arranged in subfieldsaccording to a first legacy communication protocol; generating, at thenetwork interface device, a second portion of the PHY preamble accordingto a second communication protocol, wherein the second portion of thePHY preamble is generated to include a repetition of the signal field;and generating, at the network interface device, a PHY data unit thatincludes the PHY preamble, the PHY data unit for transmission via awireless communication channel.

In another embodiment, a wireless network interface device having one ormore integrated circuits configured to: generate a first legacy portionof a physical layer (PHY) preamble, wherein the first legacy portion ofthe PHY preamble is generated to include a signal field having PHYparameters arranged in subfields according to a first legacycommunication protocol, generate a second portion of the PHY preambleaccording to a second communication protocol, wherein the second portionof the PHY preamble is generated to include a repetition of the signalfield, and generate a PHY data unit that includes the PHY preamble.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram of an example wireless local area network(WLAN) 10, according to an embodiment;

FIGS. 2A and 2B are diagrams of a prior art orthogonal frequencydivision multiplexing (OFDM) short range data unit;

FIG. 3 is a diagram of another prior art OFDM short range data unit;

FIG. 4 is a diagram of another OFDM short range data unit;

FIG. 5 is a diagram of another prior art OFDM short range data unit;

FIG. 6 is a set of diagrams illustrating modulation of various preamblefields as defined by the IEEE 802.11n Standard;

FIG. 7 is a set of diagrams illustrating modulation used to modulatesymbols of a prior art data unit;

FIG. 8 is a diagram of a prior art single carrier (SC) short range dataunit;

FIG. 9 is a diagram of a normal mode OFDM long range data unit that,according to an embodiment;

FIG. 10 is a diagram of a normal mode OFDM long range data unit that,according to another embodiment;

FIG. 11 is a diagram of a normal mode OFDM long range data unit that,according to another embodiment;

FIG. 12 is a diagram of a normal mode OFDM long range data unit that,according to another embodiment;

FIG. 13 is a diagram of a normal mode OFDM long range data unit that,according to another embodiment;

FIG. 14 is a block diagram of an example PHY processing unit forgenerating normal mode data units, according to an embodiment;

FIG. 15A is a block diagram of an example PHY processing unit forgenerating control mode data units, according to an embodiment;

FIG. 15B is a block diagram of an example PHY processing unit forgenerating control mode data units, according to another embodiment;

FIG. 16A is a diagram of an example signal field format, according to anembodiment;

FIG. 16B is a diagram of a block encoded signal field of FIG. 16A,according an embodiment;

FIG. 17A is a diagram of an another example signal field format,according to another embodiment;

FIG. 17B is a diagram of a block encoded signal field of FIG. 17A,according an embodiment;

FIG. 17C is a diagram of an another example signal field format,according to yet another embodiment;

FIG. 17D is a diagram of an another example signal field format,according to still another embodiment;

FIG. 18A is a block diagram of an example PHY processing unit forgenerating control mode data units, according to another embodiment;

FIG. 18B is a block diagram of an example PHY processing unit forgenerating control mode data units, according to another embodiment;

FIG. 19A is a block diagram of an example PHY processing unit forgenerating control mode data units, according to yet another embodiment;

FIG. 19B is a block diagram of an example PHY processing unit forgenerating control mode data units, according to another embodiment;

FIG. 20A is a diagram of a signal field of a control mode data unit,according to an embodiment;

FIG. 20B is a diagram of a signal field of a control mode data unit,according to another embodiment;

FIG. 20C is a diagram of a data portion of a control mode data unit,according to an embodiment;

FIG. 20D is a diagram of a data portion of a control mode data unit,according to another embodiment;

FIG. 21 is a diagram of an example control mode data unit which includesa longer preamble compared to a preamble included in a normal mode dataunit, according to an embodiment;

FIG. 22A is a diagram of a long training field of a normal mode dataunit, according to an embodiment;

FIG. 22B is a diagram a long training field of a control mode data unit,according to an embodiment;

FIG. 23 is a diagram of a control mode OFDM data unit, according to anembodiment;

FIG. 24 is a diagram of a control mode OFDM data unit, according toanother embodiment;

FIGS. 25A and 25B are diagrams of a short training sequence subfield anda short training sequence subfield included in a control preamble and anormal mode preamble, respectively, according to an embodiment;

FIG. 25C illustrates frequency domain values corresponding to a shorttraining sequence of FIG. 25A, according to an embodiment;

FIGS. 26A-26B are diagrams of a control mode short training sequence anda normal mode short training sequence, respectively, according to anembodiment;

FIG. 26C illustrates frequency domain values corresponding to the shorttraining sequence of FIG. 26A, according to an embodiment;

FIGS. 27A and 27B are diagrams of a control mode data unit and a normalmode data unit, respectively, according to an embodiment;

FIGS. 28A-28B are diagrams of a control mode data unit and a normal modedata unit, respectively, according to another embodiment;

FIGS. 29A-29B are diagrams of a control mode data unit and a normal modedata unit, respectively, according to another embodiment;

FIGS. 30A-30B are diagrams of a control mode data unit and a normal modedata unit, respectively, according to another embodiment;

FIGS. 31A-31B are diagrams of a control mode preamble and a normal modepreamble, respectively, according to another embodiment;

FIGS. 32A-32B are diagrams of a control mode preamble and a normal modepreamble, respectively, according to another embodiment;

FIGS. 33A-33B are diagrams of a normal mode preamble and a control modepreamble, respectively, according to another embodiment;

FIG. 33C is a diagram of a control mode preamble, according to anotherembodiment.

FIGS. 34A-34B are diagrams of a control mode preamble and a normal modepreamble, respectively, according to another embodiment;

FIG. 35 is a flow diagram of an example method for generating a dataunit, according to an embodiment; and

FIG. 36 is a flow diagram of an example method for generating dataunits, according to an embodiment.

DETAILED DESCRIPTION

In embodiments described below, a wireless network device such as anaccess point (AP) of a wireless local area network (WLAN) transmits datastreams to one or more client stations. The AP is configured to operatewith client stations according to at least a first communicationprotocol. The first communication protocol defines operation in a sub 1GHz frequency range, and is typically used for applications requiringlong range wireless communication with relatively low data rates. Thefirst communication protocol (e.g., IEEE 802.11 of or IEEE 802.11ah) isreferred to herein as a “long range” communication protocol. In someembodiments, the AP is also configured to communicate with clientstations according to one or more other communication protocols whichdefine operation in generally higher frequency ranges and are typicallyused for closer-range communications with higher data rates. The higherfrequency communication protocols (e.g., IEEE 802.11a, IEEE 802.11n,and/or IEEE 802.11ac) are collectively referred to herein as “shortrange” communication protocols.

In some embodiments, the physical layer (PHY) data units conforming tothe long range communication protocol (“long range data units”) are thesame as or similar to data units conforming to a short rangecommunication protocol (“short range data units”), but are generatedusing a lower clock rate. To this end, in an embodiment, the AP operatesat a clock rate suitable for short range operation, and down-clocking isused to generate a clock to be used for the sub 1 GHz operation. As aresult, in this embodiment, a data unit that conforms to the long rangecommunication protocol (“long range data unit”) maintains a physicallayer format of a data unit that conforms to a short range communicationprotocol (short range data unit”), but is transmitted over a longerperiod of time. In addition to this “normal mode” specified by the longrange communication protocol, in some embodiments, the long rangecommunication protocol also specifies a “control mode” with a reduceddata rate compared to the lowest data rate specified for the normalmode. Because of the lower data rate, the control mode further extendscommunication range and generally improves receiver sensitivity. In someembodiments, the AP utilizes the control mode in signal beacon orassociation procedures and/or in transmit beamforming trainingoperations, for example. Additionally or alternatively, the AP utilizesthe control mode in situations in which longer range transmission isneeded and a lower data rate is acceptable, such as, for example, tocommunicate with a smart meter or a sensor which periodically transmitssmall amounts of data (e.g., measurement readings) over a long distance.

FIG. 1 is a block diagram of an example wireless local area network(WLAN) 10, according to an embodiment. An AP 14 includes a hostprocessor 15 coupled to a network interface 16. The network interface 16includes a medium access control (MAC) processing unit 18 and a physicallayer (PHY) processing unit 20. The PHY processing unit 20 includes aplurality of transceivers 21, and the transceivers 21 are coupled to aplurality of antennas 24. Although three transceivers 21 and threeantennas 24 are illustrated in FIG. 1, the AP 14 can include differentnumbers (e.g., 1, 2, 4, 5, etc.) of transceivers 21 and antennas 24 inother embodiments.

The WLAN 10 includes a plurality of client stations 25. Although fourclient stations 25 are illustrated in FIG. 1, the WLAN 10 can includedifferent numbers (e.g., 1, 2, 3, 5, 6, etc.) of client stations 25 invarious scenarios and embodiments. At least one of the client stations25 (e.g., client station 25-1) is configured to operate at leastaccording to the long range communication protocol. In some embodiments,at least one of the client stations 25 (e.g., client station 25-4) is ashort range client station that is configured to operate at leastaccording to one or more of the short range communication protocols.

The client station 25-1 includes a host processor 26 coupled to anetwork interface 27. The network interface 27 includes a MAC processingunit 28 and a PHY processing unit 29. The PHY processing unit 29includes a plurality of transceivers 30, and the transceivers 30 arecoupled to a plurality of antennas 34. Although three transceivers 30and three antennas 34 are illustrated in FIG. 1, the client station 25-1can include different numbers (e.g., 1, 2, 4, 5, etc.) of transceivers30 and antennas 34 in other embodiments.

In an embodiment, one or both of the client stations 25-2 and 25-3, hasa structure the same as or similar to the client station 25-1. In anembodiment, the client station 25-4, has a structure similar to theclient station 25-1. In these embodiments, the client stations 25structured the same as or similar to the client station 25-1 have thesame or a different number of transceivers and antennas. For example,the client station 25-2 has only two transceivers and two antennas,according to an embodiment.

In various embodiments, the PHY processing unit 20 of the AP 14 isconfigured to generate data units conforming to the long rangecommunication protocol and having formats described hereinafter. Thetransceiver(s) 21 is/are configured to transmit the generated data unitsvia the antenna(s) 24. Similarly, the transceiver(s) 24 is/areconfigured to receive the data units via the antenna(s) 24. The PHYprocessing unit 20 of the AP 14 is configured to process received dataunits conforming to the long range communication protocol and havingformats described hereinafter, according to various embodiments.

In various embodiments, the PHY processing unit 29 of the client device25-1 is configured to generate data units conforming to the long rangecommunication protocol and having formats described hereinafter. Thetransceiver(s) 30 is/are configured to transmit the generated data unitsvia the antenna(s) 34. Similarly, the transceiver(s) 30 is/areconfigured to receive data units via the antenna(s) 34. The PHYprocessing unit 29 of the client device 25-1 is configured to processreceived data units conforming to the long range communication protocoland having formats described hereinafter, according to variousembodiments.

In some embodiments, the AP 14 is configured to operate in dual bandconfigurations. In such embodiments, the AP 14 is able to switch betweenshort range and long range modes of operation. According to one suchembodiment, when operating in short range mode, the AP 14 transmits andreceives data units that conform to one or more of the short rangecommunication protocols. When operating in a long range mode, the AP 14transmits and receives data units that conform to the long rangecommunication protocol. Similarly, the client station 25-1 is capable ofdual frequency band operation, according to some embodiments. In theseembodiments, the client station 25-1 is able to switch between shortrange and long range modes of operation. In other embodiments, the AP 14and/or the client station 25-1 is dual band device that is able toswitch between different low frequency bands defined for long rangeoperations by the long range communication protocol. In yet anotherembodiment, the AP 14 and/or the client station 25-1 is single banddevice configured to operate in only one long range frequency band.

FIG. 2A is a diagram of a prior art OFDM short range data unit 200 thatthe AP 14 is configured to transmit to the client station 25-4 viaorthogonal frequency division multiplexing (OFDM) modulation, accordingto an embodiment. In an embodiment, the client station 25-4 is alsoconfigured to transmit the data unit 200 to the AP 14. The data unit 200conforms to the IEEE 802.11a Standard and occupies a 20 Megahertz (MHz)band. The data unit 200 includes a preamble having a legacy shorttraining field (L-STF) 202, generally used for packet detection, initialsynchronization, and automatic gain control, etc., and a legacy longtraining field (L-LTF) 204, generally used for channel estimation andfine synchronization. The data unit 200 also includes a legacy signalfield (L-SIG) 206, used to carry certain physical layer (PHY) parametersof with the data unit 200, such as modulation type and coding rate usedto transmit the data unit, for example. The data unit 200 also includesa data portion 208. FIG. 2B is a diagram of example data portion 208(not low density parity check encoded), which includes a service field,a scrambled physical layer service data unit (PSDU), tail bits, andpadding bits, if needed. The data unit 200 is designed for transmissionover one spatial or space-time stream in single input a single output(SISO) channel configuration.

FIG. 3 is a diagram of a prior art OFDM short range data unit 300 thatthe AP 14 is configured to transmit to the client station 25-4 viaorthogonal frequency domain multiplexing (OFDM) modulation, according toan embodiment. In an embodiment, the client station 25-4 is alsoconfigured to transmit the data unit 300 to the AP 14. The data unit 300conforms to the IEEE 802.11n Standard, occupies a 20 MHz band, and isdesigned for mixed mode situations, i.e., when the WLAN includes one ormore client stations that conform to the IEEE 802.11a Standard but notthe IEEE 802.11n Standard. The data unit 300 includes a preamble havingan L-STF 302, an L-LTF 304, an L-SIG 306, a high throughput signal field(HT-SIG) 308, a high throughput short training field (HT-STF) 310, and Mdata high throughput long training fields (HT-LTFs) 312, where M is aninteger which generally corresponds to a number of spatial streams usedto transmit the data unit 300 in a multiple input multiple output (MIMO)channel configuration. In particular, according to the IEEE 802.11nStandard, the data unit 300 includes two HT-LTFs 312 if the data unit300 is transmitted using two spatial streams, and four HT-LTFs 312 isthe data unit 300 is transmitted using three or four spatial streams. Anindication of the particular number of spatial streams being utilized isincluded in the HT-SIG field 308. The data unit 300 also includes a dataportion 314.

FIG. 4 is a diagram of a prior art OFDM short range data unit 400 thatthe AP 14 is configured to transmit to the client station 25-4 viaorthogonal frequency domain multiplexing (OFDM) modulation, according toan embodiment. In an embodiment, the client station 25-4 is alsoconfigured to transmit the data unit 400 to the AP 14. The data unit 400conforms to the IEEE 802.11n Standard, occupies a 20 MHz band, and isdesigned for “Greenfield” situations, i.e., when the WLAN does notinclude any client stations that conform to the IEEE 802.11a Standardbut not the IEEE 802.11n Standard. The data unit 400 includes a preamblehaving a high throughput Greenfield short training field (HT-GF-STF)402, a first high throughput long training field (HT-LTF1) 404, a HT-SIG406, and M data HT-LTFs 408, where M is an integer which generallycorresponds to a number of spatial streams used to transmit the dataunit 400 in a multiple input multiple output (MIMO) channelconfiguration. The data unit 400 also includes a data portion 410.

FIG. 5 is a diagram of a prior art OFDM short range data unit 500 thatthe client station AP 14 is configured to transmit to the client station25-4 via orthogonal frequency domain multiplexing (OFDM) modulation,according to an embodiment. In an embodiment, the client station 25-4 isalso configured to transmit the data unit 500 to the AP 14. The dataunit 500 conforms to the IEEE 802.11ac Standard and is designed for“Mixed field” situations. The data unit 500 occupies a 20 MHz or a 40MHz bandwidth channel. In other embodiments or scenarios, a data unitsimilar to the data unit 500 occupies a channel of a differentbandwidth, such as an 80 MHz, or a 160 MHz bandwidth channel, forexample. The data unit 500 includes a preamble having an L-STF 502, anL-LTF 504, an L-SIG 506, a first very high throughput signal field(VHT-SIG-A) 508, a very high throughput short training field (VHT-STF)510, M very high throughput long training fields (VHT-LTFs) 512, where Mis an integer, and a second very high throughput signal field(VHT-SIG-B) 512. The data unit 500 also includes a data portion 514. Insome embodiments, the data unit 500 is a multi-user data unit whichcarries information to more than one of the client stations 25simultaneously. In such embodiments or scenarios, the first VHT-SIG-Aincludes information common to all of the intended client stations, andVHT-SIG-B includes user-specific information for each of the intendedclient stations.

FIG. 6 is a set of diagrams illustrating modulation of the L-SIG,HT-SIG1, and HT-SIG2 fields as defined by the IEEE 802.11n Standard. TheL-SIG field is modulated according to binary phase shift keying (BPSK),whereas the HT-SIG1 and HT-SIG2 fields are modulated according to BPSK,but on the quadrature axis (Q-BPSK). In other words, the modulation ofthe HT-SIG1 and HT-SIG2 fields is rotated by 90 degrees as compared tothe modulation of the L-SIG field. As illustrated in FIG. 6, suchmodulation allows a receiving device to determine or auto-detect,without decoding the entire preamble, that the data unit conforms to theIEEE 802.11n Standard rather than the IEEE 802.11a Standard.

FIG. 7 is a set of diagrams illustrating modulation of the L-SIG field,the first symbol of the VHT-SIG-A field, the second symbol of theVHT-SIG-A field, and VHT-SIG-B as defined by the IEEE 802.11ac Standard.The L-SIG is modulated according to binary phase shift keying (BPSK).Similarly, first symbol of the VHT-SIGA field is modulated according toBPSK. On the other hand, the second symbol of the VHT-SIG-A field ismodulated according to BPSK, but on the quadrature axis (Q-BPSK). TheVHT-SIG-B field is modulated according to BPSK, similar to theL-SIG-field and the first symbol of the VHT-SIG-A field. Similar to the802.11n auto-detect feature discussed above, such modulation allows areceiving device to determine or auto-detect, without decoding theentire preamble, that the data unit conforms to the IEEE 802.11acStandard rather than either one of the IEEE 802.11a Standard or the IEEE802.11n Standard.

FIG. 8 is a diagram of a single carrier (SC) short range data unit 800that the client station AP 14 configured to transmit to the clientstation 25-4 via a single carrier channel, according to an embodiment.In an embodiment, the client station 25-4 is also configured to transmitthe data unit 800 to the AP 14. The data unit 800 includes a SYNC field802 that allows a receiver to detect presence of a data unit and beginsynchronizing with the incoming signal. The data 800 also includes astart frame delimiter (SFD) field 804 that signals the beginning of aframe. The SYNC field 802 and the SFD field 804 form the preambleportion of the data unit 800. The data unit 800 also includes a headerportion having a signal field (SIGNAL) 806, a service field (SERVICE)808, a length field (LENGTH) 810, and a cyclic check redundancy checkfield (CRC) 812. The data unit 800 also includes a physical layerservice data unit (PSDU), i.e., the data portion 814.

In various embodiments and/or scenarios, data units that conform to along range communication protocol (e.g., the IEEE 802.11af or 802.11ahStandard) are formatted at least substantially the same as defined bythe IEEE 802.11a Standard, the 802.11n Standard (mixed mode orGreenfield), or the 802.11ac Standard, as described and shown above inconnection with FIGS. 2-5, but are transmitted at a lower frequency(e.g., sub-1 GHz) and using a slower clock rate. In some suchembodiments, a transmitting device (e.g., the AP 14) down-clocks by afactor of N the clock rate used for generating the short range dataunits, to a lower clock rate to be used for generating the long rangedata units. The long range data unit is therefore generally transmittedover a longer time, and occupies a smaller bandwidth, than thecorresponding short range data unit. The down-clocking factor N isdifferent according to different embodiments and/or scenarios. In oneembodiment, the down-clocking factor N is equal to 10. In otherembodiments, other suitable down-clocking factor (N) values areutilized, and transmission times and bandwidths of long range data unitsare scaled accordingly. In some embodiments, the down-clocking factor Nis a power of two (e.g., N=8, 16, 32, etc.). In some embodiments, inaddition to down-clocked data units, which correspond to the “normal”,long range communication protocol also specifies a “control” mode (and acorresponding “control mode” data unit format) with a reduced data ratecompared to the lowest data rate specified for the normal mode. Examplesof normal mode data units generated using down-clocking, according tosome such embodiments, are described blow with reference to FIGS. 9-13and are also described in U.S. patent application Ser. No. 13/359,336,filed on Jan. 26, 2012, which is hereby incorporated by reference hereinin its entirety.

FIG. 9 is a diagram of an example normal mode OFDM long range data unit900 that the AP 14 is configured to transmit to the client station 25-1via orthogonal frequency domain multiplexing (OFDM) modulation,according to an embodiment. In an embodiment, the client station 25-1 isalso configured to transmit the data unit 900 to the AP 14. The dataunit 900 is similar to the data unit 500 of FIG. 5 except that the dataunit 900 is transmitted using a clock rate that is down-clocked from theshort range clock rate by a down-clocking factor N. As a result, symbolduration of each OFDM symbol of the data unit 900 is N times longercompared to symbol duration of an OFDM symbol included in the data unit500. In the embodiment of FIG. 9, N is equal to 10. Accordingly, eachOFDM symbol included in the data unit 900 is 10 times longer compared toan OFDM symbol included in the data unit 500. In other embodiments,other suitable down-clocking factors are utilized.

FIG. 10 is a diagram of an example normal mode OFDM long range data unit1000 that the AP 14 is configured to transmit to the client station 25-1via orthogonal frequency domain multiplexing (OFDM) modulation,according to an embodiment. In an embodiment, the client station 25-1 isalso configured to transmit the data unit 1000 to the AP 14. The dataunit 1000 is similar to the “green-field” data unit 400 of FIG. 4,except that the data unit 1000 is transmitted using a clock rate that isdown-clocked from the short range clock rate by a down-clocking factorN. As a result, symbol duration of each OFDM symbol of the data unit1000 is N times longer compared to symbol duration of an OFDM symbolincluded in the data unit 400. In the embodiment of FIG. 10, N is equalto 10. Accordingly, each OFDM symbol included in the data unit 1000 is10 times longer compared to an OFDM symbol included in the data unit400. In other embodiments, other suitable down-clocking factors areutilized.

FIG. 11 is a diagram of an example normal mode OFDM long range data unit1100 that the AP 14 is configured to transmit to the client station 25-1via orthogonal frequency domain multiplexing (OFDM) modulation whenoperating in a long range mode, according to an embodiment. In anembodiment, the client station 25-1 is also configured to transmit thedata unit 1100 to the AP 14. The data unit 1100 is similar to the dataunit 500 of FIG. 5, except that the data unit 1100 is transmitted usinga clock rate that is down-clocked from the short range clock rate by adown-clocking factor N. As a result, symbol duration of each OFDM symbolof the data unit 1100 is N times longer compared to symbol duration ofan OFDM symbol included in the data unit 500. In the embodiment of FIG.10, N is equal to 10. Accordingly, each OFDM symbol included in the dataunit 1100 is 10 times longer compared to an OFDM symbol included in thedata unit 500. In other embodiments, other suitable down-clockingfactors are utilized.

FIG. 12 is a diagram of an example normal mode OFDM long range data unit1200 that the AP 14 is configured to transmit to the client station 25-1via orthogonal frequency domain multiplexing (OFDM) modulation whenoperating in a long range mode, according to an embodiment. The dataunit 1200 is similar to the data unit 1100 of FIG. 11 except that thatthe legacy portion of the preamble (i.e., L-STF 1102, L-LTF 1104, L-SIG1106) is omitted from the data unit 1200. In one embodiment, theVHT-SIG-B field 1214 is omitted from the data unit 1200. Further, bitallocations for some or all fields of the data unit 1200 are differentfrom the bit allocations defined by a short range communication protocolin some embodiments.

FIG. 13 is a diagram of an example normal mode OFDM long range data unit1300 that the AP 14 is configured to transmit to the client station 25-1via orthogonal frequency domain multiplexing (OFDM) modulation whenoperating in a long range mode, according to an embodiment. In anembodiment, the client station 25-1 is also configured to transmit thedata unit 1300 to the AP 14. The data unit 1300 is similar to the dataunit 200 of FIG. 2, except that the data unit 1300 is transmitted usinga clock rate that is down-clocked from the short range clock rate by adown-clocking factor N. As a result, symbol duration of each OFDM symbolof the data unit 1300 is N times longer compared to symbol duration ofan OFDM symbol included in the data unit 200. In the embodiment of FIG.10, N is equal to 10. Accordingly, each OFDM symbol included in the dataunit 1300 is 10 times longer compared to an OFDM symbol included in thedata unit 200. In other embodiments, other suitable down-clockingfactors are utilized.

FIG. 14 is a block diagram of an example PHY processing unit 1400 forgenerating normal mode data units, according to an embodiment. Referringto FIG. 1, the AP 14 and the client station 25-1, in one embodiment,each include a PHY processing unit such as the PHY processing unit 1400.In various embodiments and/or scenarios, the PHY processing unit 1400generates long range data units such as one of the data units of FIGS.9-13, for example.

The PHY processing unit 1400 includes a scrambler 1402 that generallyscrambles an information bit stream to reduce the occurrence of longsequences of ones or zeros. An FEC encoder 1406 encodes scrambledinformation bits to generate encoded data bits. In one embodiment, theFEC encoder 1406 includes a binary convolutional code (BCC) encoder. Inanother embodiment, the FEC encoder 1406 includes a binary convolutionalencoder followed by a puncturing block. In yet another embodiment, theFEC encoder 1406 includes a low density parity check (LDPC) encoder. Aninterleaver 1410 receives the encoded data bits and interleaves the bits(i.e., changes the order of the bits) to prevent long sequences ofadjacent noisy bits from entering a decoder at the receiver. Aconstellation mapper 1414 maps the interleaved sequence of bits toconstellation points corresponding to different subcarriers of an OFDMsymbol. More specifically, for each spatial stream, the constellationmapper 1414 translates every bit sequence of length log₂(M) into one ofM constellation points.

The output of the constellation mapper 1414 is operated on by an inversediscrete Fourier transform (IDFT) unit 1418 that converts a block ofconstellation points to a time-domain signal. In embodiments orsituations in which the PHY processing unit 1400 operates to generatedata units for transmission via multiple spatial streams, the cyclicshift diversity (CSD) unit 1422 inserts a cyclic shift into all but oneof the spatial streams to prevent unintentional beamforming. The outputof the CSD unit 1422 is provided to the guard interval (GI) insertionand windowing unit 1426 that prepends, to an OFDM symbol, a circularextension of the OFDM symbol and smooths the edges of each symbol toincrease spectral decay. The output of the GI insertion and windowingunit 1426 is provided to the analog and radio frequency (RF) unit 1430that converts the signal to analog signal and upconverts the signal toRF frequency for transmission.

In various embodiments, control mode corresponds to the lowest data rateMCS of the normal mode and introduces redundancy or repetition of bitsinto at least some fields of the data unit to further reduce the datarate. For example, control mode introduces redundancy into the dataportion and/or the signal field of a control mode data unit according toone or more repetition and coding schemes described below, in variousembodiments and/or scenarios. As an example, according to an embodiment,data units in normal mode are generated according a particularmodulation and coding scheme (MCS), e.g., and MCS selected from a set ofMCSs, such as MCS0 (binary phase shift keying (BPSK) modulation andcoding rate of ½) to MCS9 (quadrature amplitude modulation (QAM) andcoding rate of ⅚), with higher order MCSs corresponding to higher datarates. Control mode data units, in one such embodiment, are generatedusing modulation and coding as defined by MCS0 and with added bitrepletion or block encoding that further reduce the data rate.

FIG. 15A is a block diagram of an example PHY processing unit 1500 forgenerating control mode data units, according to an embodiment. In someembodiments, the PHY processing unit 1500 generates signal and/or datafields of control mode data units. Referring to FIG. 1, the AP 14 andthe client station 25-1, in one embodiment, each include a PHYprocessing unit such as the PHY processing unit 1500.

The PHY processing unit 1500 is similar to the PHY processing unit 1400of FIG. 14 except that the PHY processing unit 1500 includes a blockcoding unit 1504 coupled to the scrambler 1502. In an embodiment, theblock coding unit 1504 reads incoming (scrambled) information bits oneblock at a time, generates a number of copies of each block (or each bitin a block), interleaves the resulting bits according to a coding schemeand outputs the interleaved bits for further encoding by the BCC encoder1506. Generally, each block contains the number of information bitsthat, after having been encoded by the block coding unit 1504 and by theBCC encoder 1506, fill the data tones of a single OFDM symbol, accordingto an embodiment. As an example, in one embodiment, the block codingunit 1504 generates two copies (2× repetition) of each block of 12information bits to generate 24 bits to be included in an OFDM symbol.The 24 bits are then encoded by the BCC encoder 1506 at the coding rateof ½ to generate 48 bits that modulate 48 data tones of an OFDM symbol(e.g., using BPSK modulation). As another example, in anotherembodiment, the block coding unit 1504 generates four copies (4×repetition) of each block of 6 information bits to generate 24 bitswhich are then encoded by the BCC encoder 1506 at the coding rate of ½to generate 48 bits that modulate 48 data tones of an OFDM symbol. Asyet another example, in another embodiment, the block coding unit 1504generates two copies (2× repetition) of each block of 13 informationbits to generate 26 bits which are then encoded by the BCC encoder 1506at the coding rate of ½ to generate 52 bits that modulate 52 data tonesof an OFDM symbol.

In some embodiments, the block coding unit 1504 applies a 4× repetitionscheme when generating a data (or a signal) field as defined by MCS0 asspecified in the IEEE 802.11n Standard for 20 MHz channel, i.e. with 52data tones per OFDM symbol. In this case, according to an embodiment,the block coding unit 1504 generates four copies of each block of 6information bits to generate 24 bits and then adds two padding bits(i.e., two bits of a predetermined values) to provide the specifiednumber of bits (i.e., 26 bits for 52 data tones) to the BCC encoderwhich encoded the 26 bits using the coding rate of ½ to generate 52coded bits for modulating the 52 data tones.

In one embodiment, the block coding unit 1504 utilizes a “block level”repetition scheme in which each block of n bits is repeated mconsecutive times. As an example, if m is equal to 4 (4× repetitions),the block coding unit 1504 generates a sequence [C, C, C, C], where C isa block of n bits, according to an embodiment. In another embodiment,the block coding unit 1504 utilizes a “bit level” repetition scheme inwhich each incoming bit is repeated m consecutive times. In this case,in an embodiment, if m is equal to 4 (4× repetitions), the block codingunit 1504 generates the sequence [b1 b1 b1 b1 b2 b2 b2 b2 b3 b3 b3 b3 .. . ], where b1 is the first bit in the block of bits, b2 is the secondbit, and so on. In yet another embodiment, the block coding unit 1504generates m number of copies of the incoming bits and interleaves theresulting bit stream according to any suitable code. Alternatively, instill another embodiment, the block coding unit 1504 encodes incomingbits or incoming blocks of bits using any suitable code, e.g., a Hammingblock code with the coding rate of a ½, ¼, etc., or any other block codewith the coding rate of ½, ¼, etc. (e.g., (1,2) or (1, 4) block code,(12,24) block code or (6, 24) block code, a (13,26) block code, etc.).

According to an embodiment, the effective coding rate corresponding to acombination of the coding performed by the block coding unit 1504 andcoding performed by the BCC encoder 1506 the product of the two codingrates. For example, in an embodiment in which the block coding unit 1504utilizes 4× repetition (or coding rate of ¼) and the BCC encoder 1506utilizes a coding rate of ½, the resulting effective coding rate isequal to ⅛. As a result of the reduced coding rate compared to thecoding rate used to generate a similar normal mode data unit, data ratein control mode is effectively reduced by a factor corresponding to thenumber the coding rate applied by the block coding unit 1504 (e.g., afactor of 2, a factor of 4, etc.), according to an embodiment.

According to some embodiments, the block coding unit 1504 utilizes thesame block coding scheme for generating the signal field of a controlmode data unit as the block coding scheme used for generating the dataportion of the control mode data unit. For instance, in an embodiment,an OFDM symbol of the signal field and an OFDM symbol of the dataportion each includes 48 data tones, and in this embodiment, the blockcoding unit 1504 applies a 2× repetition scheme to blocks of 12 bits forthe signal field and the data portion, for example. In anotherembodiment, the data portion and the signal field of a control mode dataunit are generated using different block coding schemes. For example, inan embodiment, the long range communication protocol specifies adifferent number of data tones per OFDM symbol in the signal fieldcompared to the number of data tones per OFDM symbol in the dataportion. Accordingly, in this embodiment, the block coding unit 1504utilizes a different block size and, in some embodiments, a differentcoding scheme, when operating on the signal field compared to the blocksize and the coding scheme used for generating the data portion. Forexample, if the long range communication protocol specifies 52 datatones per OFDM symbol of the signal field and 48 data tones per OFDMtones of the data portion, the block coding unit 1504 applies a 2×repetition scheme to blocks of 13 bits of the signal field and a 2×repetition scheme to blocks of 12 bits of the data portion, according toone embodiment.

The BCC encoder 1506 encodes the block coded information bits, accordingto an embodiment. In an embodiment, BCC encoding is performedcontinuously over the entire field being generated (e.g., the entiredata field, the entire signal field, etc.). Accordingly, in thisembodiment, information bits corresponding to the field being generatedare partitioned into blocks of a specified size (e.g., 6 bits, 12 bits,13 bits, or any other suitable number of bits), each block is processedby the block coding unit 1504, and the resulting data stream is thenprovided to the BCC encoder 1506 which continuously encodes the incomingbits.

Similar to the interleaver 1410 of FIG. 14, in various embodiments, theinterleaver 1510 changes the order of bits in order to provide diversitygain and reduce the chance that consecutive bits in a data stream willbecome corrupted in the transmission channel. In some embodiments,however, the block coding unit 1504 provides sufficient diversity gainand the interleaver 1510 is omitted.

In some embodiments, information bits in the data portion of a controlmode data unit are be padded (i.e., a number of bits of a known value isadded to the information bits) so that the data unit occupies an integernumber of OFDM symbols, for example. Referring to FIG. 1, in someembodiments, padding is implemented in the MAC processing unit 18, 28and/or the PHY processing unit 20, 29. In some such embodiments, thenumber of padding bits is determined according to padding equationsprovided in a short range communication protocol (e.g., the IEEE 802.11aStandard, the IEEE 802.11n Standard, the IEEE 802.11ac Standard, etc.).In general, these padding equations involve computing a number ofpadding bits based, in part, on a number of data bits per OFDM symbol(N_(DBPS)) and/or a number coded data bits per symbol (N_(CBPS)). Incontrol mode, according to an embodiment, the number of padding bits isdetermined based on the number of information bits in an OFDM symbol(e.g., 6 bits, 12 bits, 13 bits, etc.) before the information bits areblock encoded by the block coding unit 1504 and BCC encoded by the BCCencoder 1506. Accordingly, the number of padding bits in a control modedata unit is generally different from the number of padding bits in thecorresponding normal mode data (or in the corresponding short range dataunit). On the other hand, according to an embodiment, the number ofcoded bits per symbol is the same as the number of coded bits per symbolin normal mode data unit (or in the corresponding short range dataunit), e.g., 24, 48, 52, etc. coded bits per OFDM.

FIG. 15B is a block diagram of an example PHY processing unit 1550 forgenerating control mode data units, according to another embodiment. Insome embodiments, the PHY processing unit 1550 generates signal and/ordata fields of control mode data units. Referring to FIG. 1, the AP 14and the client station 25-1, in one embodiment, each include a PHYprocessing unit such as the PHY processing unit 1550.

The PHY processing unit 1550 is similar to the PHY processing unit 1500of FIG. 15, except that in the PHY processing unit 1550, the BCC encoder1506 is replaced by the LDPC encoder 1556. Accordingly, in thisembodiment, the output of the block coding unit 1504 is provided forfurther block encoding by the LDPC encoder 1556. In an embodiment, theLDPC encoder 1556 utilizes a block code corresponding to a coding rateof ½, or a block code corresponding to another suitable coding rate. Inthe illustrated embodiment, the PHY processing unit 1550 omits theinterleaver 1510 because adjacent bits in an information stream aregenerally spread out by the LDPC code itself and no further interleavingis needed. Additionally, in an embodiment, further frequency diversityis provided by the LDPC tone remapping unit 1560. According to anembodiment, the LDPC tone remapping unit 1560 reorders coded informationbits or blocks of coded information bits according to a tone remappingfunction. The tone remapping function is generally defined such thatconsecutive coded information bits or blocks of information bits aremapped onto nonconsecutive tones in the OFDM symbol to facilitate datarecovery at the receiver in cases in which consecutive OFDM tones areadversely affected during transmission. In some embodiments, the LDPCtone remapping unit 1560 is omitted. Referring again to FIG. 15A, invarious embodiments, a number of tail bits are typically added to eachfield of a data unit for proper operation of the BCC encoder 1506, e.g.,to ensure that the BCC encoder, after having encoded each field, isbrought back to zero state. In one embodiment, for example, six tailbits are inserted at the end of the data portion before the data portionis provided to the BCC encoder 1506 (e.g., after the bits are processedby the block coding unit 1504).

Similarly, in the case of a signal field, tail bits are inserted intothe signal field before the signal field is provided to the BCC encoder1506, in various embodiments. FIG. 16A is a diagram of an example signalfield 1600, according to an embodiment. The signal field 1600 includes afour bit rate subfield 1604, a twelve bit length subfield 1604 and onebit parity bit 1606. The signal field 1600 also includes a five bitreserved subfield 1608. In this embodiment, bit allocation of the signalfield 1600 does not include bits allocated for tail bits. FIG. 16B is adiagram of a block encoded signal field 1650, according an embodiment.In an embodiment, the block coding unit 1504 of FIG. 15 generates thesignal field 1650 by encoding the signal field 1600 of FIG. 16A. Theblock coded signal field 1650 includes four OFDM symbols 1652, whereineach OFDM symbol 1652 includes four repetitions of a block of six bitsof the signal field 1600. As illustrated, six tail bits and two paddingbits are added at the end of the last OFDM of the block encoded signalfield (OFDM symbol 1652-4).

Alternatively, tail bits are inserted into a signal field before thesignal field is block encoded, in another embodiment. Accordingly, inthis case, the inserted tail bits are repeated or otherwise encoded(e.g., by the block coding unit 1504 of FIG. 15). FIG. 17A is a diagramof a signal field 1700 in which six tail bits are inserted at the end ofthe signal field before block encoding, according to an embodiment.Signal field 1700 includes a four bit rate subfield 1702, a one bitreserved subfield 1704, a twelve bit length subfield 1706, followed byone parity bit (1708) and six tail bits (1710). FIG. 17B is a diagram ofa block encoded signal field 1750, according an embodiment. In anembodiment, the block coding unit 1504 of FIG. 15 generates the signalfield 1750 by encoding the signal field 1700 of FIG. 17A. As in theexample of the block coded signal field 1650 of FIG. 16, the signalfield 1750 includes four OFDM symbols. In this embodiment, however, theblock coded signal field 1750 includes multiple repetitions (fourrepetitions, in this case) of the tail bits.

In some embodiments, the signal field of a control mode data unit has adifferent format compared to the signal field format of a normal modedata unit. In some such embodiment, the signal field of control modedata units is shorter compared to a signal field of a normal mode dataunit. For example, only one modulation and coding scheme is used incontrol mode, according to an embodiment, and therefore less information(or no information) regarding modulation and coding needs to becommunicated in the control mode signal field. Similarly, in anembodiment, maximum length of a control mode data unit is shortercompared to a maximum length of a normal mode data unit and, in thiscase, less bits are needed for the length subfield of the control modesignal field. As an example, in one embodiment, a control mode signalfield is formatted according to the IEEE 802.11n Standard but omitscertain subfields (e.g., the low density parity check (LDPC) subfield,the space time block coding (STBC) subfield, etc.). Additionally oralternatively, in some embodiments, a control mode signal field includesa shorter CRC subfield compared to the cyclic redundancy check (CRC)subfield of a normal mode signal field (e.g., less than 8 bits). Ingeneral, in control mode, certain signal field subfields are omitted ormodified and/or certain new information is added, according to someembodiments.

FIG. 17C is diagram of a control mode signal field 1760, according toone such embodiment. The control mode signal field 1760 is similar tothe signal field 1700 of FIG. 17A, but the rate subfield is omitted fromthe signal field 1760 (e.g., because only one rate is specified forcontrol mode). Additionally, the signal field 1760 includes a number ofspace time streams (Nsts) subfield 1764 for signaling null data packetsin a channel sounding procedure, for example.

FIG. 17D is diagram of a control mode signal field 1770, according toanother embodiment. The signal field 1770 is similar to the signal field1700 of FIG. 17A, but omits a rate field, includes a null data packetfield (NDP) 1772 for signaling null data packets in a channel soundingprocedure, for example. The signal field 1770 also includes anindication of the number of space time streams in the length field 1774.

FIG. 18A is a block diagram of an example PHY processing unit 1800 forgenerating control mode data units, according to another embodiment. Insome embodiments, the PHY processing unit 1800 generates signal and/ordata fields of control mode data units. Referring to FIG. 1, the AP 14and the client station 25-1, in one embodiment, each include a PHYprocessing unit such as the PHY processing unit 1800.

The PHY processing unit 1800 is similar to the PHY processing unit 1500of FIG. 15, except that in the PHY processing unit 1800 the block codingunit 1809 is located after the BCC encoder (1806). Accordingly, in thisembodiment, information bits are first encoded by the BCC encoder 1806and the BCC coded bits are then replicated or otherwise block encoded bythe block coding unit 1808. As in the example embodiment of the PHYprocessing unit 1500, in an embodiment, processing by the BCC encoder1806 is performed continuously over the entire field being generated(e.g., the entire data portion, the entire signal field, etc.).Accordingly, in this embodiment, information bits corresponding to thefield being generated are first encoded by the BCC encoder 1806 and theBCC coded bits are then partitioned into blocks of a specified size(e.g., 6 bits, 12 bits, 13 bits, or any other suitable number of bits).Each block is then processed by the block coding unit 1808. As anexample, in one embodiment, the BCC encoder 1806 encodes 12 informationbits per OFDM symbol using the coding rate of ½ to generate 24 BCC codedbits and provides the BCC coded bits to the block coding unit 1808. Inan embodiment, the block coding unit 1808 generates two copies of eachincoming block and interleaves the generated bits according to a codingscheme to generate 48 bits to be included in an OFDM symbol. In one suchembodiment, the 48 bits correspond to 48 data tones generated using aFast Fourier Transform (FFT) of size 64 at the IDFT processing unit1818. As another example, in another embodiment, the BCC encoder 1806encodes 6 information bits per OFDM symbol using the coding rate of ½ togenerate 12 BCC coded bits and provides the BCC coded bits to the blockcoding unit 1808. In an embodiment, the block coding unit 1808 generatestwo copies of each incoming block and interleaves the generated bitsaccording to a coding scheme to generate 24 bits to be included in anOFDM symbol. In one such embodiment, the 24 bits correspond to 24 datatones generated using an FFT of size 32 at the IDFT processing unit1818.

Similar to the block coding unit 1504 of FIG. 15, the repetition andcoding scheme used by the block coding unit 1808 to generate the signalfield of a control mode data unit, depending on an embodiment, is thesame as or different from the repetition and coding scheme used by theblock coding unit 1808 to generate the data portion of the control modedata unit. In various embodiments, the block coding unit 1808 implementsa “block level” repetition scheme or a “bit level” repetition scheme asdiscussed above in regard to the block coding unit 1504 of FIG. 15.Similarly, in another embodiment, the block coding unit 1808 generates mnumber of copies of the incoming bits and interleaves the resulting bitstream according to a suitable code, or otherwise encodes incoming bitsor incoming blocks of bits using any suitable code, e.g., a Hammingblock code with the coding rate of a ½, ¼, etc., or any other block codewith the coding rate of ½, ¼, etc. (e.g., (1,2) or (1, 4) block code,(12,24) block code or (6, 24) block code, a (13,26) block code, etc.).

The effective coding rate for data units generated by the PHY processingunit 1800 is a product of the coding rate used by the BCC encoder 1806and the number of repetitions (or the coding rate) used by the blockcoding unit 1808, according to an embodiment.

In an embodiment, the block coding unit 1808 provides sufficientdiversity gain such that no further interleaving of coded bits isneeded, and the interleaver 1810 is omitted. One advantage of omittingthe interleaver 1810 is that in this case OFDM symbols with 52 datatones can be generated using 4× or a 6× repetition schemes even thoughin some such situations the number of data bits per symbol is not aninteger. For example, in one such embodiment, the output of the BCCencoder 1806 is partitioned into blocks of 13 bits and each block isrepeated four times (or block encoded with a rate of ¼) to generate 52bits to be included in an OFDM symbol. In this case, if the BCC encoderutilizes a coding rate of ½, the number of data bits per symbol is equal6.5. In an example embodiment utilizing 6× repetition, the BCC encoder1806 encodes information bits using a coding rate of ½ and the output ispartitioned into blocks of four bits. The block coding unit 1808 repeatseach four bit block six times (or block encodes each block using acoding rate of ⅙) and adds four padding bits to generate 52 bits to beincluded in an OFDM symbol.

As in the example of the PHY processing unit 1500 of FIG. 15 discussedabove, if padding is used by the PHY processing unit 1800, the number ofdata bits per symbol (N_(DBPS)) used for padding bit computations is theactual number of non-redundant data bits in an OFDM symbol (e.g., 6bits, 12 bits, 13 bits as in the example above, or any other suitablenumber of bits). The number of coded bits per symbol (N_(CBPS)) used inpadding bit computations is equal to the number of bits actuallyincluded in an OFDM symbol (e.g., 24 bits, 48 bits, 52 bits, or anyother suitable number of bits included in an OFDM symbol).

Also as in the example of the PHY processing unit 1500 of FIG. 15, anumber of tail bits are typically inserted into each field of a dataunit for proper operation of the BCC encoder 1806, e.g., to ensure thatthe BCC encoder, after having encoded each field, is brought back tozero state. In one embodiment, for example, six tail bits are insertedat the end of the data portion before the data portion is provided tothe BCC encoder 1806 (i.e., after processing by the block coding unit1504 is performed). Similarly, in the case of a signal field, tail bitsare inserted at the end of the signal field before the signal field isprovided to the BCC encoder 1806, according to an embodiment. In anexample embodiment in which the block coding unit 1808 utilizes a 4×repetition scheme (or another block code with the coding rate of ¼), theBCC encoder 1806 utilizes the coding rate of ½, and the signal fieldincludes 24 information bits (including tail bits), the 24 signal fieldbits are BCC encoded to generate 48 BCC encoded bits which are thenpartitioned into four blocks of 12 bits each for further encoding by theblock coding unit 1808. Accordingly, in this embodiment, the signalfield is transmitted over four OFDM symbols each of which includes 6information bits of the signal field.

As discussed above with regard to FIGS. 15-17, in some embodiments, thesignal field of a control mode data unit is shorter (i.e. includes lessbits) compared to a signal field of a normal mode data unit.Accordingly, in these embodiments, less OFDM symbols are generallyneeded to transmit the signal field compared to embodiments in which alonger signal field is generated using the same repetition and codingscheme.

Further, in some embodiments, the PHY processing unit 1800 generatesOFDM symbols with 52 data tones according to the MCS0 specified in theIEEE 802.11n Standard or the IEEE 802.11ac Standard and the block codingunit 1808 utilizes a 4× repetition scheme. In some such embodiments,extra padding is used to ensure that the resulting encoded data streamto be included in an OFDM symbol includes 52 bits. In one suchembodiment, padding bits are added to coded information the bits afterthe bits have been processed by the block coding unit 1808.

In the embodiment of FIG. 18, the PHY processing unit 1800 also includesa peak to average power ratio (PAPR) reduction unit 1809. In anembodiment, the peak to average power ratio unit reduction 1809 flipsthe bits in some or all repeated blocks to reduce or eliminate theoccurrence of the same bit sequences at different frequency locations inan OFDM symbol thereby reducing the peak to average power ratio of theoutput signal. In general, bit flipping involves changing the bit valueof zero to the bit value of one and changing the bit vale of one to thebit value of zero. According to an embodiment, the PAPR reduction unit1809 implements bit flipping using an XOR operation. For example, in anembodiment utilizing 4× repetition of a block of coded bits, if a blockof coded bits to be included in an OFDM symbols is denoted as C and ifC′=C XOR 1 (i.e., block C with bits flipped), then some possible bitsequences at the output of the PAPR reduction unit 1809, according tosome embodiments, are [C C′ C′ C′], [C′ C′ C′ C], [C C′ C C′], [C C CC′], etc. In general, any combination of block with bits flipped andblocks with bits not flipped can be used. In some embodiments, the PAPRunit 1809 is omitted.

FIG. 18B is a block diagram of an example PHY processing unit 1850 forgenerating control mode data units, according to another embodiment. Insome embodiments, the PHY processing unit 1850 generates signal and/ordata fields of control mode data units. Referring to FIG. 1, the AP 14and the client station 25-1, in one embodiment, each include a PHYprocessing unit such as the PHY processing unit 1850.

The PHY processing unit 1850 is similar to the PHY processing unit 1800of FIG. 18, except that in the PHY processing unit 1850, the BCC encoder1506 is replaced by the LDPC encoder 1856. Accordingly, in thisembodiment, information bits are first encoded by the LDPC encoder 1856and the LDPC coded bits are then replicated or otherwise block encodedby the block coding unit 1808. In an embodiment, the LDPC encoder 1856utilizes a block code corresponding to a coding rate of ½, or a blockcode corresponding to another suitable coding rate. In the illustratedembodiment, the PHY processing unit 1850 omits the interleaver 1810because adjacent bits in an information stream are generally spread outby the LDPC code itself and, according to an embodiment, no furtherinterleaving is needed. Additionally, in an embodiment, furtherfrequency diversity is provided by the LDPC tone remapping unit 1860.According to an embodiment, the LDPC tone remapping unit 1860 reorderscoded information bits or blocks of coded information bits according toa tone remapping function. The tone remapping function is generallydefined such that consecutive coded information bits or blocks ofinformation bits are mapped onto nonconsecutive tones in the OFDM symbolto facilitate data recovery at the receiver in cases in whichconsecutive OFDM tones are adversely affected during transmission. Insome embodiments, the LDPC tone remapping unit 1860 is omitted.

FIG. 19A is a block diagram of an example PHY processing unit 1900 forgenerating control mode data units, according to another embodiment. Insome embodiments, the PHY processing unit 1900 generates signal and/ordata fields of control mode data units. Referring to FIG. 1, the AP 14and the client station 25-1, in one embodiment, each include a PHYprocessing unit such as the PHY processing unit 1900.

The PHY processing unit 1900 is similar to the PHY processing unit 1800of FIG. 18 except that in the PHY processing unit 1900 the block codingunit 1916 is located after the constellation mapper 1914. Accordingly,in this embodiment, BCC encoded information bits, after having beenprocessed by the interleaver 1910, are mapped to constellation symbolsand the constellation symbols are then replicated or otherwise blockencoded by the block coding unit 1916. According to an embodiment,processing by the BCC encoder 1906 is performed continuously over theentire field being generated (e.g., the entire data field, the entiresignal field, etc.). In this embodiment, information bits correspondingto the field being generated are first encoded by the BCC encoder 1806and the BCC coded bits are then mapped to constellation symbols by theconstellation mapper 1914. The constellation symbols are thenpartitioned into blocks of a specified size (e.g., 6 symbols, 12symbols, 13 symbols, or any other suitable number of symbols) and eachblock is then processed by the block coding unit 1916. As an example, inan embodiment utilizing 2× repetition, the constellation mapper 1914generates 24 constellation symbols and the block coding unit 1916generates two copies of the 24 symbols to generate 48 symbolscorresponding to 48 data tones of an OFDM symbol (e.g., as specified inthe IEEE 802.11a Standard). As another example, in an embodimentutilizing 4× repetition, the constellation mapper 1914 generates 12constellation symbols and the block coding unit 1916 generates fourcopies of the 12 constellation symbols to generate 48 symbolscorresponding to 48 data tones of an OFDM symbol (e.g., as specified inthe IEEE 802.11a Standard). As yet another example, in an embodimentutilizing 2× repetition, the constellation mapper 1914 generates 26constellation symbols and the block coding unit 1916 repeats the 26symbols (i.e., generates two copies of the 26 symbols) to generate 52symbols corresponding to 52 data tones of an OFDM symbol (e.g., asspecified in the IEEE 802.11n Standard or the IEEE 802.11ac Standard).In general, in various embodiments and/or scenarios, the block codingunit 1916 generates any suitable number of copies of blocks of incomingconstellation symbols and interleaves the generated symbols according toany suitable coding scheme. Similar to the block coding unit 1504 ofFIG. 15 and the block coding unit 1808 of FIG. 18, the repetition andcoding scheme used by the block coding unit 1916 to generate a signalfield (or signal fields) of a control mode data unit is, depending onthe embodiment, the same as or different from the repetition and codingscheme used by the block coding unit 1916 to generate the data portionof the control mode data unit.

The effective coding rate for data units generated by the PHY processingunit 1900 is a product of the coding rate used by the BCC encoder 1906and the number of repetitions (or the coding rate) used by the blockcoding unit 1916, according to an embodiment.

According to an embodiment, because redundancy in this case isintroduced after the information bits have been mapped to constellationsymbols, each OFDM symbol generated by the PHY processing unit 1900includes less non-redundant data tones compared to OFDM data tonesincluded in a normal mode data units. Accordingly, the interleaver 1910is designed to operate on less tones per OFDM symbol compared to theinterleaver used in the normal mode (such as the interleaver 1410 ofFIG. 14), or the interleaver used in generating the corresponding shortrange data unit. For example, in an embodiment with 12 non-redundantdata tones per OFDM symbol, the interleaver 1910 is designed using thenumber of columns (Ncol) of 6 and the number of rows (Nrow) of 2*thenumber of bits per subcarrier (Nbpscs). In another example embodimentwith 12 non-redundant data tones per OFDM symbol, the interleaver 1910is designed using Ncol of 4 and Nrow of 3*Nbpscs. In other embodiments,other interleaver parameters different from interleaver parameter usedin the normal mode are utilized for the interleaver 1910. Alternatively,in an embodiment, the block coding unit 1916 provides sufficientdiversity gain such that no further interleaving of coded bits isneeded, and the interleaver 1910 is omitted. In this case, as in theexample embodiment utilizing the PHY processing unit 1800 of FIG. 18,OFDM symbols with 52 data tones can be generated using 4× or a 6×repetition schemes even though in some such situations the number ofdata bits per symbol is not an integer.

As in the example embodiment of the PHY processing unit 1500 of FIG. 15or the PHY processing unit 1800 of FIG. 18 discussed above, if paddingis used by the PHY processing unit 1900, the number of data bits persymbol (N_(DBPS)) used for padding bit computations is the actual numberof non-redundant data bits in an OFDM symbol. (e.g., 6 bits, 12 bits, 13bits as in the example above, or any other suitable number of bits). Thenumber of coded bits per symbol (N_(CBPS)) used in padding bitcomputations is equal to the number of non-redundant bits included in anOFDM symbol which, in this case, corresponds to number of bits in theblock of constellation symbols processed by the block coding unit 1916(e.g., 12 bits, 24 bits, 26 bits, etc.).

Also as in the example embodiment of the PHY processing unit 1500 ofFIG. 15 discussed above, a number of tail bits are typically insertedinto each field of a data unit for proper operation of the BCC encoder1906, e.g., to ensure that the BCC encoder, after having encoded eachfield, is brought back to zero state. In one embodiment, for example,six tail bits are inserted at the end of the data portion before thedata portion is provided to the BCC encoder 1906. Similarly, in the caseof a signal field, tail bits are inserted at the end of the signal fieldbefore the signal field is provided to the BCC encoder 1906, accordingto an embodiment. In an example embodiment in which the block coding1916 utilizes a 4× repetition scheme (or another block code with thecoding rate of ¼), the BCC encoder 1906 utilizes the coding rate of ½,and the signal field includes 24 information bits (including tail bits),the 24 signal field bits are BCC encoded to generate 48 BCC encoded bitswhich are then mapped to constellation points by the constellationmapper 1914. The constellation points are then partitioned into fourblocks of 12 bits each for further processing by the block coding unit1808. Accordingly, in this embodiment, the signal field is transmittedover four OFDM symbols each of which includes 6 information bits of thesignal field.

As discussed above with regard to FIGS. 15-17, in some embodiments, thesignal field of a control mode data unit is shorter (i.e., includes lessbits) compared to a signal field of a normal mode data unit.Accordingly, in these embodiments, less OFDM symbols are generallyneeded to transmit the signal field compared to a longer signal fieldgenerated using the same repetition and coding scheme.

In some embodiments, the PHY processing unit 1900 generates OFDM symbolswith 52 data tones according to the MCS0 specified in the IEEE 802.11nStandard or the IEEE 802.11ac Standard and the block coding unit 1916utilizes a 4× repetition scheme. In some such embodiments, extra paddingis used to ensure that the resulting encoded data stream to be includedin an OFDM symbol includes 52 bits. In one such embodiment, padding bitsare added to coded information the bits after the bits have beenprocessed by the block coding unit 1808.

In the embodiment of FIG. 19, the PHY processing unit 1900 includes apeak to average power ratio (PAPR) reduction unit 1917. In anembodiment, the peak to average power ratio unit 1917 adds a phase shiftto some of the data tones modulated with repeated constellations. Forexample, in one embodiment the added phase shift is 180 degrees. The 180degree phase shift corresponds to a sign flip of the bits that modulatethe data tones for which phase shifts are implemented. In anotherembodiment, the PAPR reduction unit 1917 adds a phase shift that isdifferent than 180 degrees (e.g., a 90 degree phase shift or any othersuitable phase shift). As an example, in an embodiment utilizing 4×repetition, if a block of 12 constellation symbols to be included in anOFDM symbols is denoted as C and if simple block repetition isperformed, the resulting sequence is [C C C C]. In some embodiments, thePAPR reduction unit 1917 introduces a sign flip (i.e., -C) or a 90degree phase shift (i.e., j*C) for some of the repeated blocks. In somesuch embodiments, the resulting sequence is, for example, [C -C -C -C],[-C -C -C -C], [C -C C -C], [C C C -C], [C j*C, j*C, j*C], or any othercombination of C, -C, j*C, and -j*C. In general, any suitable phaseshift can be introduced in any repeated block in various embodimentsand/or scenarios. In some embodiments, the PAPR reduction unit 1809 isomitted.

In some embodiments, the PHY processing unit 1900 generates OFDM symbolswith 52 data tones according to the MCS0 specified in the IEEE 802.11nStandard or the IEEE 802.11ac Standard and the block coding 1916utilizes a 4× repetition scheme. In some such embodiments, extra pilottones are inserted to ensure that the resulting number of data and pilottones in an OFDM symbol is equal to 56 as specified in the short rangecommunication protocol. As an example, in an embodiment, six informationbits are BCC encoded at the coding rate of ½ and the resulting 12 bitsare mapped to 12 constellation symbols (BPSK). The 12 constellationsymbols modulate 12 data tones which are then repeated four times thegenerated 48 data tones. Four pilot tones are added as specified in theIEEE 802.11n Standard and 4 extra pilot tones are added to generate 56data and pilot tones.

FIG. 19B is a block diagram of an example PHY processing unit 1950 forgenerating control mode data units, according to another embodiment. Insome embodiments, the PHY processing unit 1950 generates signal and/ordata fields of control mode data units. Referring to FIG. 1, the AP 14and the client station 25-1, in one embodiment, each include a PHYprocessing unit such as the PHY processing unit 1950.

The PHY processing unit 1950 is similar to the PHY processing unit 1900of FIG. 19, except that in the PHY processing unit 1950, the BCC encoder1906 is replaced by the LDPC encoder 1956. Accordingly, in thisembodiment, LDPC encoded information bits are mapped to constellationsymbols by the constellation mapper 1914 and the constellation symbolsare then replicated or otherwise block encoded by the block coding unit1916. In an embodiment, the LDPC encoder 1956 utilizes a block codecorresponding to a coding rate of ½, or a block code corresponding toanother suitable coding rate. In the illustrated embodiment, the PHYprocessing unit 1950 omits the interleaver 1910 because adjacent bits inan information stream are generally spread out by the LDPC code itselfand, according to an embodiment, no further interleaving is needed.Additionally, in an embodiment, further frequency diversity is providedby the LDPC tone remapping unit 1960. According to an embodiment, theLDPC tone remapping unit 1960 reorders coded information bits or blocksof coded information bits according to a tone remapping function. Thetone remapping function is generally defined such that consecutive codedinformation bits or blocks of information bits are mapped ontononconsecutive tones in the OFDM symbol to facilitate data recovery atthe receiver in cases in which consecutive OFDM tones are adverselyaffected during transmission. In some embodiments, the LDPC toneremapping unit 1960 is omitted.

In the embodiments described above with regard to FIGS. 15-19, thecontrol mode introduces redundancy by repeating bits in frequencydomain. Alternatively, in some embodiments, OFDM symbol repetition ofthe signal and/or data fields of control mode data units is performed intime domain. For example, FIG. 20A illustrates a 2× repetition of eachOFDM symbol of HT-SIG1 and HT-SIG2 fields in a preamble of a controlmode data unit, according to an embodiment. Similarly, FIG. 20Billustrates a 2× repetition of each OFDM symbol of the L-SIG field in apreamble of a control mode data unit, according to an embodiment.

FIG. 20C illustrates a time domain repetition scheme for OFDM symbols inthe data portion of a control mode data unit, according to oneembodiment. FIG. 20D illustrates a repetition scheme for OFDM symbols inthe data portion, according to another embodiment. As illustrated, inthe embodiment of FIG. 20C OFDM symbol repetitions are outputcontinuously, while in the embodiment of FIG. 20D OFDM symbolrepetitions are interleaved. In general, OFDM symbol repetitions areinterleaved according to any suitable interleaving scheme, in variousembodiments and/or scenarios.

According to an embodiment utilizing a time domain repetition scheme,pilot tone signs are changed from one tone to the next as specified inthe IEEE 802.11a or the IEEE 802.11n, for example. Accordingly, in suchembodiments, pilot tones in a repeated OFDM symbol are not the same asin the incoming (original) OFDM symbol in at least some situations.

In some embodiments, the preamble used for a control mode data unit(“control mode preamble”) is different compared to the preamble used fora normal mode data unit (“normal mode preamble”). For instance, acontrol mode preamble includes a longer long training sequence forbetter channel estimation or a longer short training sequence for betterpacket detection and synchronization at a receiving device, in someembodiments. In some embodiments, a control mode preamble includes anextra preamble in addition or the normal mode preamble. Further, in someembodiments in which the control mode preamble is different from thenormal mode preamble, the control mode preamble is generated such that areceiver is able to determine or auto-detect whether the incoming dataunit corresponds to the control mode or to the normal mode and thereforeis able to properly decode the data unit.

FIG. 21 is a diagram of an example control mode data unit 2100 whichincludes a longer preamble compared to a preamble included in a normalmode data unit, according to an embodiment. The control PHY data unit2100 is similar to the normal PHY data unit 1000 of FIG. 10, except thatHT-LTF2 field 2108 is longer than each HT-LTF field 1012 of the normalPHY data unit 1000. More specifically, the data unit 2100 includes anHT-LTF2 field 2108 that occupies two OFDM symbols and is transmittedover 80 μs, compared to one OFDM symbol and 40 μs used to transmit eachHT-LTF field 1012 of the normal PHY data unit 1000.

In an embodiment, a long training field is extended (e.g., byintroducing a number of repetitions of the long training sequence usedin the normal mode) to span any suitable number of OFDM symbols. FIGS.22A and 22B illustrate an example embodiment in which more repetitionsof a long training sequence are included in a control mode preamble thanin a normal mode preamble. In particular, FIG. 22A illustrates a longtraining field 2200 of a normal mode data unit, according to anembodiment. The long training field 2200 includes a double guardinterval (DGI) 2202 and two repetitions of a long training sequence2204. In one embodiment, DGI is equal to 2×0.8 μs, for example. Inanother embodiment, a DGI of another suitable value is utilized. Asindicated in FIG. 22A, in the illustrated embodiment, duration of thelong training field of a normal mode data unit is 8N μs, where N is thedown-clock ratio used to generate the data unit.

FIG. 22B is a diagram a long training field 2500 of a control mode dataunit, according to an embodiment. The long training field 2500 includesa new guard interval (New GI) field 2502 and eight repetitions of a longtraining sequence 2504. In one embodiment, the New GI duration isgreater than the normal mode DGI duration in the data unit 2200. Inanother embodiment, New GI duration is the same as the DGI duration inthe data unit 2200. As indicated in FIG. 22B, in the illustratedembodiment, the duration of the control mode long training field 2500 is64N μs. In other embodiments, other suitable numbers of repetition of along training sequence are utilized and accordingly long training fieldsof other suitable lengths are generated in normal mode and/or in controlmode, where a control mode LTF field is longer than a normal mode LTFfield by any suitable factor.

In another embodiment, a control mode preamble includes an extrapreamble in addition to a regular preamble included in the normal modedata units. FIG. 23 is a diagram of a control mode OFDM data unit 2300,according to one such embodiment. The data unit 2300 is similar to thenormal mode data unit 1300 of FIG. 13, except that the data unit 2300includes a single carrier (SC) extra preamble portion 2302. The extra SCpreamble 2202 includes a SYNC field 2204 and a SFD field 2206. In anembodiment, the SC preamble of the data unit 2300 is at leastsubstantially the same as PLCP preamble 814 of the data unit 800 (FIG.8), down-clocked by the same down-clocking factor N as the down-clockingfactor used to generate the OFDM portion 2312. In another embodiment, adown-clocking factor used for the SC preamble portion 2302 is differentfrom the down-clocking factor used for the OFDM portion 2212.

FIG. 24 is a diagram of a control mode OFDM data unit 2400 utilizing anextra preamble in control mode, according to another embodiment. Thedata unit 2400 is similar to the data unit 2200 of FIG. 22, except thatthe SYNC field 2204 is replace by the Golay code field 2304 in FIG. 24.In some embodiments, the Golay code field includes a number ofrepetitions of a Golay complementary sequence (GCS), for example. Thenumber of repetitions is determined based on the particular Golaysequence length utilized and the overall preamble length of the dataunit 1600, in an embodiment. In some embodiments, Golay sequences oflength 16, 32, 64, 128, or any other suitable length are utilized. Insome embodiments, the long range communication protocol defines a longpreamble and a short preamble, each consisting of a different number ofGolay sequence repetitions. In one such embodiment, differentcomplimentary sequences are utilized for the long and the short preamblecases (e.g., Ga sequence for the long preamble, and Gb sequence for theshort preamble) to allow a receiver determine which type of preamble areceived data unit includes. Generally, the two complementary sequencesGa and Gb have correlation properties suitable for detection at areceiving device. For example, the complementary spreading sequences Gaand Gb may be selected so that the sum of corresponding out-of-phaseaperiodic autocorrelation coefficients of the sequences Ga and Gb iszero. In some embodiments, the complementary sequences Ga and Gb have azero or almost-zero periodic cross-correlation. In another aspect, thesequences Ga and Gb may have aperiodic cross-correlation with a narrowmain lobe and low-level side lobes, or aperiodic auto-correlation with anarrow main lobe and low-level side lobes.

In some embodiments which include an SC extra preamble portion, forwider bandwidth OFDM data units (e.g., 40 MHz, 80 MHz, 160 MHz, etc.),the SC preamble is repeated in each down-clocked 20 MHz sub-band. Insome embodiments, particularly when the single carrier extra preamble isgenerated using a clock rate that is different from the clock rate usedto generated the OFDM portion of the data preamble, the SC/OFDM boundaryrequirement is defined as specified in the IEEE 802.11g Standard fordirect sequence spread spectrum (DSSS) and OFDM boundary requirement. Inan embodiment, the start frame delimiter (SFD) field (e.g., SFD field2306 in FIG. 23, SFD field 2406 in FIG. 24) is used to determine the endof the extra SC preamble. In some embodiments, the STF field (i.e.,field 2308 in FIG. 23, filed 2408 in FIG. 24) is omitted.

In some embodiments, the control mode preamble includes an extendedshort training field of a normal mode preamble. The longer shorttraining field is used to improve packet detection and better syncing atthe receiver, for example. In one such embodiment, the number of periodsincluded in a short training field of a control mode preamble is greaterthan the number of periods included in a normal mode preamble. Inanother embodiment, duration of each period in a short training field ofa control mode preamble is longer compared to the duration of eachperiod in a short training field of a normal mode preamble. In anotherembodiment, the number of periods included in a short training field ofa control mode preamble is greater than the number of periods includedin a normal mode preamble and each period in the control mode shorttraining field is longer compared to each period in the normal modeshort training field.

FIGS. 25A and 25B are diagrams of a short training sequence subfield2500 and a short training sequence subfield 2550 included in a controlpreamble and a normal mode preamble, respectively, according to anembodiment. As illustrated, in this embodiment, duration of each periodof the short training field 2500 is greater than duration of each periodof the short training field 2550 by a factor of two. In an embodiment,the longer short training sequence is generated by including morenon-zero tones in each OFDM symbol of a control mode short trainingsequence compared to the number of non-zero tones included in each OFDMsymbol of a normal mode short training field. In general, each period ofa short training sequence does not include a repetition pattern.Therefore, in an embodiment, the longer short training sequence of acontrol mode preamble will not trigger a correlator that is used fordetecting normal mode data units at a receiving device. In other words,this format allows a receiving device to differentiate between the twomodes based on repetition pattern detection in an Inverse Fast FourierTransform (IFFT) window at the receiving device.

FIG. 25C illustrates frequency domain values corresponding to the shorttraining sequence 2500, according to an embodiment. As illustrated inFIG. 25C, in this embodiment, each OFDM symbol of the short trainingfield 2550 includes non-zero values corresponding to the +/−8 OFDM toneindices. In one embodiment, the values of the two non-zero tones aresuch that p(−8)!=p(8) and p(−8)!=−p(8). In general, any values for whichthese criteria are satisfied are used as specific non-zero tone values,in various embodiments and/or scenarios. As an example, in oneembodiment, the specific values for the two non-zero tones are definedas:

[p(8), p(−8)]=a*sqrt(2), 1+j]  Equation 1

where a is a scaling factor.

FIGS. 26A-26B are diagrams of a control mode short training sequence2600 and a normal mode short training sequence 2650, respectively,according to an embodiment. In the embodiment of FIGS. 26A-26B, acontrol mode preamble includes a short training sequence of the sameperiod as the short training sequence of a normal mode preamble, butincludes more repetitions of the sequence compared to the number ofrepetitions included in the normal mode preamble. In an embodiment, theshort training sequence in the training field 2650 are encoded accordingto a predefined code (e.g., alternating +/−1 for consecutiverepetitions, or any other suitable predetermined code) thereby allowinga receiving device to distinguish between control mode and normal modedata units based on the short training field.

FIG. 26D illustrates frequency domain values corresponding to the shorttraining sequence 2600 of FIG. 26A in an embodiment in which alternating+1/−1 is applied across the short training sequence repetitions of theshort training field 2600, according to an embodiment. In theillustrated embodiment, each OFDM symbol of the short training field2600 includes non-zero values corresponding to the −12, −4, 4, and 12OFDM tone indices. In various embodiments, the specific values of thenon-zero tones are such that the values are not equal to each other inabsolute value (i.e., non-periodic). As an example, in one embodiment,the specific values of the four non-zero tones are defined as:

[p(−12), p(−4), p(4), p( 12 )]=a*[−1−j, −1−j, 1+j, −1−j]  Equation 2

where a is a scaling factor.

In another embodiment in which alternating +1/−1 is applied across theshort training sequence repetitions of the short training field, thealternating signs in consecutive training sequence repetitions incontrol mode are generated by shifting non-zero tones in the sequence tothe right or to the left in frequency domain by two tones, for example.As an example, if non-zero tone values are at tones [4, 8, 12, . . . ,24, −4, −8, . . . , −24] in a normal mode short training sequence, thena control mode short training sequence is generated by shifting thenormal mode non-zero tones by two with new non-zero tone locations of[6, 10, 14, . . . , 26, −2, −6, . . . , −22] or shifted to the left withnew non-zero tone locations of [2, 6, 10, 14, . . . , 22, −6, −10, . . ., −22, −26]. In another embodiment, in addition to shifting non-zerotones, extra non-zero tones are added in the control mode short trainingsequence to generate a longer sequence. For example, two extra non-zerotones are added at tone locations 2 and −26, in the example in whichnon-zero tones are shifted to the right, or at tone locations 26, −2 inthe example in which non-zero tones are shifted to the left. In otherembodiments, different suitable number of non-zero tones is added in acontrol mode short training sequence (e.g., 4, 6, 8, etc.), and theadded non-zero tones are at other suitable tone locations. Further, invarious embodiments, the non-zero tones are of any suitable values.

In an embodiment in which the control mode utilizes a single carrierextra preamble in control mode (e.g., data unit 2300 of FIG. 23, dataunit 2400 of FIG. 24), a receiver auto-detects whether an incoming dataunit is a control mode or a normal mode data unit based on whether theinitial signal of the preamble is a single carrier signal or an OFDMsignal. In some embodiments, however, a normal mode data unit as well asa control mode data unit includes an extra single carrier preamble.FIGS. 27A and 27B illustrate a control mode data unit 2700 and a normalmode data unit 2750, respectively, according to one such embodiment. Inthis embodiment, auto-detection at the receiver is based on thedifferent Golay code sequences (GCS) in the control mode and the normalmode data unit. For example, in an embodiment, a length-16 Ga sequenceis used for the single carrier preamble portion 2706 of the control modedata unit 2700, while a length-16 Gb sequence is used for the singlecarrier preamble portion 2754 of the normal mode data unit 2750.

FIGS. 28A-28B illustrate a control mode data unit 2800 and a normal modedata unit 2850, respectively, according to another embodiment in which asingle carrier extra preamble is utilized in the control mode as well asin the normal mode. In this embodiment, each the SC preamble portions2806 and the SC preamble portion 2854 is generated using the same GCSsequence (e.g., Ga), and auto-detection is based on the cover codeapplied to the corresponding delimiter field 2806 and 2856 (e.g., a signflip is applied or a different sequence is used for the control modethan for the normal mode).

FIGS. 29A-29B illustrate a control mode data unit 2900 and a normal modedata unit 2950, respectively, according to an embodiment in which areceiving device can distinguish between the two modes based onmodulation of the long training field. To this end, in the control modedata unit 2900, the phase of each tone in the field second OFDM symbolof the LTF (2906-2) is shifted (e.g., by pi, pi/2, −pi/2, or any othersuitable factor) compared to the phase of the corresponding OFDM tone ofthe first OFDM symbol of the LTF (2956-1). On the other hand, no phaseshift is introduced for the second symbol of the LTF field (2956-2) ofthe normal mode data unit 2950.

In some embodiments, mode auto-detection at a receiving device is basedon the modulation of certain preamble fields. FIGS. 30A-30B illustrate acontrol mode preamble 3000 and a normal mode preamble 3050,respectively, according to one such embodiment. The control modepreamble 3000 includes a short training field (STF) 3002, a longtraining field (LTF) 3004, a first signal field (SIG1) 3006, and asecond signal field (SIG2) 3008. Similarly, the normal mode preamble3050 includes a short training field (STF) 3052, a long training field(LTF) 3054 and a first signal field (SIG1) 3056 and a second signalfield (SIG2) 3058. In this embodiment, the control mode preamble STFfield 3002 is longer than the normal mode preamble STF field 3052. Inanother embodiment, the control mode preamble STF field 3002 is the samelength as the normal mode preamble STF field 3052. Similarly, thecontrol mode preamble LTF field 3004, depending on the embodiment, islonger than or the same length as the normal mode preamble LTF field3504.

With continued reference to FIGS. 30A-30B, each of the two control modepreamble signal fields is generated using one of the block codingschemes or a time domain repetition scheme discussed above. As a result,in this embodiment, each signal field in the control mode preamble (SIG13006 and SIG2 3008) spans two OFDM symbols, while each signal field inthe normal mode preamble (SIG1 3056 and SIG2 3058) spans one OFDMsymbol. In another embodiment, each of the control mode signal fields3006 and 3008 spans four OFDM symbols or any other suitable number ofOFDM symbols. In the embodiment of FIGS. 30A-30B, each signal field ofthe normal mode preamble (SIG1 3056 and SIG2 3058) is modulated usingQPSK modulation. The second symbol of the first signal filed of thecontrol mode preamble, which is received at the same time after the longtraining field as the second signal field of the normal mode preamble,is modulated using BPSK modulation. Accordingly, in this embodiment, areceiving device is able to auto-detect whether a data unit correspondsto the control mode or to the normal mode based on the modulation ofsecond OFDM symbol after the LTF field. In another embodiment, the firstOFDM symbol of the first signal field is modulated according to amodulation technique that is different from the modulation techniqueused for modulating the signal fields of a normal mode preamble.

FIGS. 31A-31B illustrate a control mode preamble 3100 and a normal modepreamble 3150, respectively, according to another embodiment. In thisembodiment, data units are generated using a short range communicationprotocol mixed mode preamble format (e.g., data unit 900 of FIG. 9), andmode auto-detecting is based on the different modulation techniquescorresponding to the control mode preamble L-SIG field 3106 (in thisembodiment, QPSK) and the normal mode preamble L-SIG field 3156 (in thisembodiment, BPSK).

FIGS. 32A-32B illustrate a control mode preamble 3200 and a normal modepreamble 3250, respectively, according to another embodiment. In theillustrated embodiment, normal mode data units are generated using ashort range communication protocol green field preamble format (e.g.,IEEE 802.11n Standard greenfield preamble format) and control mode dataunit are generated using the IEEE 802.11a Standard preamble formatutilizing a block coding or a repetition scheme described above. In thisembodiment mode auto-detecting is based on the different modulationtechniques corresponding to the control mode preamble L-SIG field 3206(in this embodiment, BPSK) and the normal mode preamble HT-SIG field3256 (in this embodiment, QPSK).

FIGS. 33A-33B illustrate a normal mode preamble 3300 and a control modepreamble 3350, respectively, according to another embodiment. In theillustrated embodiment, the normal mode preamble 3350 includes morerepetitions of a long training sequence than the normal mode preamble3300. In particular, in this embodiment, the normal mode preamble 3300includes two repetitions of the long training sequence 3304 while thecontrol mode preamble 3354 includes three or more repetitions of longtraining sequence 3554. Accordingly, in this embodiment, the signalfield 3306 of the normal mode preamble is received at the same point intime (relative to the beginning of the preamble) as the third LTS 3554-3of the control mode preamble. In the illustrated embodiment, the signalfield 3306 is modulated using QBPSK modulation, and the LTS 3554-4 ismodulated using BPSK modulation allowing a receiver to auto-detect themode based on the different modulation techniques.

FIG. 33C is a diagram of another control mode preamble 3370, accordingto another embodiment. The control mode preamble 3370 is similar to thecontrol mode preamble 3350 of FIG. 33B, but includes a guard intervalbefore each repeated long training sequence. In an embodiment, in thiscase, the same mode auto-detection scheme as discussed above in respectto FIGS. 33A-33B is used to distinguish between the normal mode preamble3300 and the control mode preamble 3370.

FIGS. 34A-34B illustrate a control mode preamble 3400 and a normal modepreamble 3450, respectively, according to another embodiment. In thisembodiment, the control mode preamble 3450 includes a short trainingsequence with a different period compared to the period of the shorttraining sequence of the normal mode preamble 3400, and also includesmore repetitions of the long training sequence as in the control modepreamble 3350 of FIG. 33B or the control mode preamble 3370 of FIG. 3C.As illustrated, mode auto-detection in this embodiment is based on themodulation of the signal field 3408 and the long training sequence3454-3 in the manner described above with respect to FIGS. 33A-33C.

FIG. 35 is a flow diagram of an example method 3500 for generating adata unit, according to an embodiment. With reference to FIG. 1, themethod 3500 is implemented by the network interface 16, in anembodiment. For example, in one such embodiment, the PHY processing unit20 is configured to implement the method 3500. According to anotherembodiment, the MAC processing 18 is also configured to implement atleast a part of the method 3500. With continued reference to FIG. 1, inyet another embodiment, the method 3500 is implemented by the networkinterface 27 (e.g., the PHY processing unit 29 and/or the MAC processingunit 28). In other embodiments, the method 1700 is implemented by othersuitable network interfaces.

At block 3502 information bits to be included in the data unit areencoded according to a block code. In one embodiment, information bitsare encoded using a block level or a bit level repetition schemedescribed above with respect to the block coding unit 1504 of FIG. 15,for example. At block 3604, the information bits are encoded using anFEC encoder, such as the BCC encoder 1506 of FIG. 15A, or the LDPCencoder 1556 of FIG. 15B, for example. At block 3506, information bitsare mapped to constellation symbols. At block 3508, a plurality OFDMsymbols is generated to include the constellation points. The data unitis then generated to include the OFDM symbols at block 3510.

In one embodiment, as illustrated in FIG. 35, information bits areencoded using a block encoder first (block 3502) and the block codedbits are then encoded using a BCC encoder (block 3504), such asdescribed above with respect to FIG. 15A, for example. In anotherembodiment, the order of blocks 3502 and 3504 is interchanged.Accordingly, in this embodiment, information bits are BCC encoded firstand the BCC encoded bits are encoded according to a block coding scheme,such as described above with respect to FIG. 18A, for example. In yetanother embodiment, block 3502 is positioned after block 3506. In thisembodiment, information bits are BCC encoded at block 3504, the BCCencoded bits are mapped to constellation symbols at block 3506, and theconstellation symbols are then encoded according to a block coding orrepetition scheme, such as described above with respect to FIG. 19A, forexample, at block 3502.

FIG. 36 is a flow diagram of an example method 3600 for generating dataunits, according to an embodiment. With reference to FIG. 1, the method3600 is implemented by the network interface 16, in an embodiment. Forexample, in one such embodiment, the PHY processing unit 20 isconfigured to implement the method 3600. According to anotherembodiment, the MAC processing 18 is also configured to implement atleast a part of the method 3600. With continued reference to FIG. 1, inyet another embodiment, the method 3600 is implemented by the networkinterface 27 (e.g., the PHY processing unit 29 and/or the MAC processingunit 28). In other embodiments, the method 1700 is implemented by othersuitable network interfaces.

At block 3602, a first preamble for a first data unit is generated. Inan embodiment, a normal mode preamble is generated. In an embodiment,the normal mode preamble 3050 of FIG. 30B or the normal mode preamble3300 of FIG. 33A is generated, for example. In another embodiment, apreamble conforming to another suitable format is generated. In anembodiment, the first preamble includes a long training field and asignal field. The signal field is modulated according to a modulationtechnique (e.g., BPSK, QPSK, or another suitable modulation technique.)

At block 3606, the second data unit is generated according to the seconddata unit format (e.g., a normal mode data unit).

At block 3606, a second preamble is generated. In an embodiment, acontrol mode preamble is generated. For example, the control modepreamble 3050 of FIG. 30A, the control mode preamble 3350 of FIG. 33B,or the control mode preamble 3370 of FIG. 33C is generated. In anotherembodiment, a preamble conforming to another suitable format isgenerated. In an embodiment, the second preamble includes a control modesignal field, such as the signal field 1600 of FIG. 16A, the signalfield 1700 of FIG. 17C, or the signal field 1780 of FIG. 17C, forexample, or another suitable signal field. In an embodiment, the secondsignal field is generated according to the format of the first signalfield and using one of the repetition or block coding schemes discussedabove. As a result, duration of the second signal field is longer thanthe duration of the first signal field. The second preamble alsoincludes a second long training field which includes a number ofrepetitions of a long training sequence. In some embodiment, the numberof repetitions of the long training sequence is greater that the numberof long training sequence repetitions in the first long training field(generated at block 3602).

In an embodiment, a portion of the second signal field is modulatedaccording to a modulation technique different from the modulationtechnique used for generating the first signal field (at block 3602) sothat a receiver is able to auto-detect that the second data unit (e.g.,control mode data unit) is formatted according to a second data unitformat (e.g., control mode data unit format). In another embodiment, thesecond long training field is modulated according to a modulationtechnique different from the modulation technique used for generatingthe first signal field (at block 3602) so that a receiver is able toauto-detect that the second data unit (e.g., control mode data unit) isformatted according to a second data unit format (e.g., normal mode dataunit format).

At block 3606, the second data unit is generated according to the seconddata unit format (e.g., a control mode data unit).

At least some of the various blocks, operations, and techniquesdescribed above may be implemented utilizing hardware, a processorexecuting firmware instructions, a processor executing softwareinstructions, or any combination thereof. When implemented utilizing aprocessor executing software or firmware instructions, the software orfirmware instructions may be stored in any computer readable memory suchas on a magnetic disk, an optical disk, or other storage medium, in aRAM or ROM or flash memory, processor, hard disk drive, optical diskdrive, tape drive, etc. Likewise, the software or firmware instructionsmay be delivered to a user or a system via any known or desired deliverymethod including, for example, on a computer readable disk or othertransportable computer storage mechanism or via communication media.Communication media typically embodies computer readable instructions,data structures, program modules or other data in a modulated datasignal such as a carrier wave or other transport mechanism. The term“modulated data signal” means a signal that has one or more of itscharacteristics set or changed in such a manner as to encode informationin the signal. By way of example, and not limitation, communicationmedia includes wired media such as a wired network or direct-wiredconnection, and wireless media such as acoustic, radio frequency,infrared and other wireless media. Thus, the software or firmwareinstructions may be delivered to a user or a system via a communicationchannel such as a telephone line, a DSL line, a cable television line, afiber optics line, a wireless communication channel, the Internet, etc.(which are viewed as being the same as or interchangeable with providingsuch software via a transportable storage medium). The software orfirmware instructions may include machine readable instructions that,when executed by the processor, cause the processor to perform variousacts.

When implemented in hardware, the hardware may comprise one or more ofdiscrete components, an integrated circuit, an application-specificintegrated circuit (ASIC), etc.

While the present invention has been described with reference tospecific examples, which are intended to be illustrative only and not tobe limiting of the invention, changes, additions and/or deletions may bemade to the disclosed embodiments without departing from the scope ofthe claims.

What is claimed is:
 1. A method, comprising: generating, at a networkinterface device, a first legacy portion of a physical layer (PHY)preamble, wherein the first legacy portion of the PHY preamble isgenerated to include a signal field having PHY parameters arranged insubfields according to a first legacy communication protocol;generating, at the network interface device, a second portion of the PHYpreamble according to a second communication protocol, wherein thesecond portion of the PHY preamble is generated to include a repetitionof the signal field; and generating, at the network interface device, aPHY data unit that includes the PHY preamble, the PHY data unit fortransmission via a wireless communication channel.
 2. The method ofclaim 1, wherein: generating the first legacy portion of the PHYpreamble includes generating the signal field to span only a firstsingle orthogonal frequency domain multiplexing (OFDM) symbol; andgenerating the second portion of the PHY preamble includes generatingthe repetition of the signal field to span only a second single OFDMsymbol.
 3. The method of claim 1, wherein: the first single OFDM symbolis adjacent to the second single OFDM symbol.
 4. The method of claim 2,wherein: generating the repetition of the signal field includesutilizing a first modulation that is rotated in phase by 90 degrees withrespect to a second modulation utilized with respect to the signal fieldin the first legacy portion of the PHY preamble.
 5. The method of claim4, wherein: generating the signal field in the first legacy portion ofthe PHY preamble includes utilizing binary phase shift keying (BPSK)modulation; and generating the repetition of the signal field includesutilizing BPSK modulation on a quadrature axis (Q-BPSK).
 6. The methodof claim 2, wherein: generating the repetition of the signal fieldincludes utilizing a same modulation as utilized with respect to thesignal field in the first legacy portion of the PHY preamble.
 7. Themethod of claim 6, wherein: generating the signal field in the firstlegacy portion of the PHY preamble includes utilizing binary phase shiftkeying (BPSK) modulation; and generating the repetition of the signalfield includes utilizing BPSK modulation.
 8. The method of claim 1,wherein: the signal field is a first signal field; and the secondportion of the PHY preamble is generated to include a second signalfield having PHY parameters arranged in subfields according to thesecond communication protocol.
 9. The method of claim 1, wherein: thePHY preamble is a first PHY preamble; the signal field is a first signalfield; the PHY data unit is a first PHY data unit; and the methodfurther comprises: generating, at the network interface device, a secondPHY preamble according to the first legacy communication protocol or athird legacy communication protocol, wherein the second PHY preambleincludes a second signal field having PHY parameters arranged insubfields according to the first legacy communication protocol, andgenerating, at the network interface device, a second PHY data unit thatincludes the second PHY preamble, wherein the second PHY data unit isgenerated such that the second PHY data unit does not include arepetition of the second signal field.
 10. The method of claim 9,wherein: the second PHY preamble is generated according to the thirdlegacy communication protocol; and the second PHY preamble is generatedto include a third signal field having PHY parameters arranged insubfields according to the third legacy communication protocol.
 11. Anapparatus, comprising: a wireless network interface device having one ormore integrated circuits configured to generate a first legacy portionof a physical layer (PHY) preamble, wherein the first legacy portion ofthe PHY preamble is generated to include a signal field having PHYparameters arranged in subfields according to a first legacycommunication protocol, generate a second portion of the PHY preambleaccording to a second communication protocol, wherein the second portionof the PHY preamble is generated to include a repetition of the signalfield, and generate a PHY data unit that includes the PHY preamble. 12.The apparatus of claim 11, wherein the one or more integrated circuitsare configured to: generate the signal field to span only a first singleorthogonal frequency domain multiplexing (OFDM) symbol; and generate therepetition of the signal field to span only a second single OFDM symbol.13. The apparatus of claim 11, wherein the one or more integratedcircuits are configured to: generate the PHY data unit such that thefirst single OFDM symbol is adjacent to the second single OFDM symbol.14. The apparatus of claim 12, wherein the one or more integratedcircuits are configured to: generate the repetition of the signal fieldutilizing a first modulation that is rotated in phase by 90 degrees withrespect to a second modulation utilized with respect to generating thesignal field in the first legacy portion of the PHY preamble.
 15. Theapparatus of claim 14, wherein the one or more integrated circuits areconfigured to: generate the signal field in the first legacy portion ofthe PHY preamble utilizing binary phase shift keying (BPSK) modulation;and generate the repetition of the signal field utilizing BPSKmodulation on a quadrature axis (Q-BPSK).
 16. The apparatus of claim 12,wherein the one or more integrated circuits are configured to: generatethe repetition of the signal field utilizing a same modulation asutilized with respect to generating the signal field in the first legacyportion of the PHY preamble.
 17. The apparatus of claim 16, wherein theone or more integrated circuits are configured to: generate the signalfield in the first legacy portion of the PHY preamble utilizing binaryphase shift keying (BPSK) modulation; and generate the repetition of thesignal field utilizing BPSK modulation.
 18. The apparatus of claim 11,wherein: the signal field is a first signal field; and the one or moreintegrated circuits are configured to generate the second portion of thePHY preamble to include a second signal field having PHY parametersarranged in subfields according to the second communication protocol.19. The apparatus of claim 11, wherein: the PHY preamble is a first PHYpreamble; the signal field is a first signal field; the PHY data unit isa first PHY data unit; and the one or more integrated circuits areconfigured to: generate a second PHY preamble according to the firstlegacy communication protocol or a third legacy communication protocol,wherein the second PHY preamble is generated to include a second signalfield having PHY parameters arranged in subfields according to the firstlegacy communication protocol, and generate a second PHY data unit thatincludes the second PHY preamble, wherein the second PHY data unit isgenerated such that the second PHY data unit does not include arepetition of the second signal field.
 20. The apparatus of claim 19,wherein: the second PHY preamble is generated according to the thirdlegacy communication protocol; and the one or more integrated circuitsare configured to generate the second PHY preamble to include a thirdsignal field having PHY parameters arranged in subfields according tothe third legacy communication protocol.